The petrochemical, food, and beverage processing industries use a variety of process, transportation, and storage vessels which must be periodically cleaned. Typically, such vessels or tanks are cleaned by a tank cleaning device which uses the cleaning fluid being sprayed within the tank to drive the nozzle spray assembly in a predetermined pattern. A device of this type generally includes a primary drive shaft which is connected to an impeller at an inlet end and connected at the other end to a gear box. The device includes a receiving chamber which receives high pressure fluid entering into the device and a separate secondary chamber which is defined by the gear box. As the high speed cleaning solution enters the inlet section of the tank cleaning device it flows through the impeller causing it to rotate, in turn rotating the primary drive shaft.
The gear box includes a series of gears which reduce the high speed input from the primary drive shaft to a low speed output. This reduction can be as great as 1000:1. The main housing of the tank cleaning device is connected to the output of the gear box and rotates relative to the gear box about a center axis along which the cleaning solution enters the device. The cleaning solution exits the device through a pair of opposing nozzles which rotate in a plane parallel to the center axis as the main housing of the tank cleaning device is rotated about the center axis. The spray pattern thus generated covers an infinite surface area, i.e., an outwardly projecting spherical spray pattern is thus created.
There are two basic tank cleaning devices of the above-described type. One type of tank cleaning device employs a sealed gear box. In this device, a high speed seal is provided in the wall between the receiving chamber and the gear box through which the primary shaft passes. A lubricant such as oil is provided in the gear box for keeping the gears lubricated and thus reducing the wear on the gears. A drawback of this type of tank cleaning device, however, is that due to the high speed rotation of the primary shaft, and the often severe chemical nature of the cleaning solution being passed through the device, the seal and bearing tend to wear out rapidly, requiring frequent replacement. Thus, the repair and replacement of such seals have become important factors in the maintenance of such devices.
The second type of tank cleaning device is known as a flow through device. In this device, the gear box is not sealed. Rather, the cleaning solution is allowed to flow through the gear box. In this type of device, the tank cleaning solution acts as the lubricant for the gears. Because tank cleaning solutions are poor lubricants, the gears in this type of tank cleaning device wear out much more frequently than the gears in devices employing a sealed gear box and thus require frequent repair and/or replacement. This latter type of tank cleaning device is typically used to clean tanks in the food and beverage industries which are under strict FDA (Food and Drug Administration) regulations to provide a sterile environment for the food or beverage being contained within the tank.
Because the seals in the tank cleaning devices employing a sealed gear box usually ultimately fail, the oil from these gear boxes leaks into the receiving chamber and thus can contaminate the cleaning solution. Therefore, the tank cleaning devices of the sealed gear box type are not typically used for cleaning tanks used in the food and beverage industry. It is desirable to provide a tank cleaning device for the food and beverage industry which requires little or no maintenance and does not contaminate the cleaning solution.
U.S. Pat. No. 5,092,523 proposes a solution to the problem of oil leaking into the receiving chamber. In this solution, oil is prevented from leaking into the receiving chamber by separating the gear box from the primary drive shaft. This is accomplished by providing a wall between the receiving chamber and the gear box. The torque from the primary drive shaft is transmitted to a secondary shaft in the gear box through a magnetic coupling which couples the primary shaft to the secondary shaft without physically connecting the shafts. Thus, the opening which is typically formed in the gear box to accommodate the drive shaft is sealed in this device so that no oil can leak out of the gear box in the location of the primary shaft. However, oil may still leak out of the gear box in this device. The output shaft of the gear box, which is coupled to the main housing and allows the main housing to rotate relative to the gear box, is sealed to the gear box with an O-ring which can fail and thus create a source of leakage.
A further drawback of known tank cleaning devices is that they are very heavy and thus difficult for tank cleaning personnel to transport. Typical tank cleaning devices weigh between 35 and 50 lbs. This is because the main housing and most of the other components of these devices are formed of bronze or steel. These materials have traditionally been used in these devices because they are strong, chemically resistant and heat resistant. Bronze is also conductive which is important especially for tank cleaning devices which are used in the petrochemical industry.
The carbon atoms in petrochemicals carry a positive charge. If these atoms are excited they can create an electrical current which unless grounded can be dangerous to tank cleaning personnel. The impact by the high velocity cleaning solution on oil residue in a tank being cleaned, for example, can excite the charge in the carbon atoms to the point of creating an electrical current. This current is conducted through the metal housing of the tank cleaning devices, through the steel fibers reinforcing the solution supply hose coupled to the tank cleaning device to ground. It is desirable to reduce the overall weight of tank cleaning devices while at the same time maintain the strength, chemical resistance, heat resistance and conductive properties of known steel devices.
The present invention is directed to overcoming or at least minimizing some of the problems mentioned above.